This subject comes up every other year or so. The small but noticeable dings and scratches that occur from speaker placement, sliding glass doors on the Beosound 3200, children, falling books, or curious guests.
The aluminum plates are very well anodized, as mentioned above. There are, or were BEOWORLD members here that specialize in working with the anodized front plates to the Beolab 4. Many members have changed from coloured plates to the bare, " raw, original metal " appearance of the Alu on Alu look. I would speak with these experienced members.
On the other hand there are products out there that should not be used to conceal or salvage a scratch on the BL 4000 metal. The Steel wool, nail polish, or 60 grit sandpaper effect comes to mind.